The invention provides an automatic skin taping machine designed particularly for use in applying a protective coating to the highly polished surface of aluminum sheeting used in aircraft fabrication. The invention, however, may be adapted for other uses that require the application of a film to a relatively smooth surface. The invention is especially useful in working with sheets of material having a highly polished or sensitive surface as the invention provides a completely automated, hands-off film application system that avoids any contact with the sheet surface until the protective coating is applied.
As known in the aircraft industry, temporary protective coatings are applied to aluminum sheeting in order to protect the highly polished surface of the aluminum sheets during the fabrication process. This highly polished surface is used to form the outer surface on an aircraft and provides the finished aircraft with a mirror finish that has less drag and a shiny appearance. In order to preserve this mirror finish, the polished surface must be protected during transportation, fabrication, and construction of the aircraft outer surface parts. At the mill, the aluminum sheets are packaged with a foam protective layer covering the polished surface, and the aluminum sheets are delivered to the fabricator in palletized stacks with the foam layer interspersed between each aluminum sheet. In order to be adequately protected during fabrication, however, the polished surface of the aluminum sheets must be protected with a coating, such as a tape or film, that is adhered to the polished surface and that may be later removed. Indeed, the aircraft industry has developed specifications relating to the types of coating that may be used. One example of such specifications for coating materials is the Boeing Company's aircraft specification number 5034 which lists the various types of approved coating materials. Included therein are various types of films which are mostly vinyl-based products with a removable or nonadhering adhesive. Various types of tapes that generally have a paper backing with an adhesive that becomes somewhat adhering over time are also included. For both the films and the tapes, it is critical to apply them to the sheet as close to the point in time when the part will be fabricated as possible to avoid difficulty in removing them.
The aircraft industry has also developed specifications for the handling of the aluminum sheeting and the application of the approved coatings. The polished surface of the aluminum sheeting is so sensitive that it can't even be touched with human hands and workers must use cotton gloves to handle the sheets. Any slight scratch or abrasion of the surface must be polished out before the sheet of aluminum can be used. The application of the protective coating, therefore, must be performed in a manner so as to avoid any contact with the polished surface to keep from blemishing or marring the surface. Further, the protective coating must be applied uniformly over the surface and without any significant number of air bubbles or creases in the coating. Creases or air bubbles in the coating can result in marring of the surface during fabrication as tiny pieces of aluminum from the router or saw may lodge in the pockets and eventually scratch the polished surface.
Due to the care required, the application of the protective coating in accordance with the specifications can be a somewhat slow and painstaking process. One system of application used in the past included the manual application of the tape or film by laying it out over an aluminum sheet and applying it by hand. In the tape coatings, any air bubbles or creases could be worked out by hand, but in the films, air bubbles or creases are difficult to work out by hand. The manual application of the coatings is labor intensive and requires extensive care in handling the sheets.
Another application system commonly used in the aircraft industry involves the use of a machine with a pair of oppositely rotating rollers. In using such a device, the aluminum sheets are lifted one at a time by hand and pushed in between the rollers, and the top roller applies the coating to the aluminum sheet. The sheet must be handled on both ends, i.e., into and out of the rollers, and it is significant that the applicator is stationary while the sheets are passed through the applicator. The disadvantages of such a system are that it requires handling of each sheet and touching the polished surface prior to it being protected.
In contrast, the present invention provides an automatic system for applying the protective coatings without the need for handling each sheet, and further, it avoids any contact with the polished surface until the protective coating has been applied.